This invention relates generally to multiple devices having systems capable of linking between other device systems, wherein a first system may provide services to a second linked system. More particularly, the present invention relates to devices capable of establishing or terminating a link between first and second systems dependant upon whether a predefined minimum level of quality of service can be provided by the first system to the second linked system. The predefined minimum level of quality of service is defined by the second system, wherein the definition is independent of the system requirements or hardware configuration of the first system.
Over the years, the ability of multiple devices having computer based control systems to, for example, xe2x80x9ccommunicatexe2x80x9d with one another has become increasingly important both economically and otherwise. This communication between devices requires transmitting information from one device to another. The quality of the communication transfer or transmission may be characterized by several factors including the latency (the time between the transmission of the information and its reception), reliability (the proportion of transmitted messages that are received) and security (freedom from interception, destruction, or intentional alteration by a third party). Each of these variables may be critical to an adequate communication between the devices depending upon the type of communication being transmitted. For example, latency is critical to video conferencing, reliability is critical in aircraft avionics and security is critical in electronic banking.
At times, the transmitting device may require a xe2x80x9cguaranteexe2x80x9d that a communication mechanism with the receiving device can provide a minimum quality of communication service before transmitting or communicating information to the receiving device. In the past, inherent in the definition of quality of service has been a recognition that the quality of communication service will be limited by the system constraints or hardware configuration of the receiving device. When the system or hardware of the communication mechanism is upgraded, the transmitting device or at least the definition of the quality of communication service may also need to be upgraded in order to continue communication with the receiving device via the upgraded mechanism or to utilize the improvements to the communication mechanism. Hence, although a communication mechanism""s system constraints or hardware configuration may potentially affect the quality of communication service, it is desirable that the minimum threshold of quality of communication service with the receiving device be defined independent of the communication mechanism""s system constraints or hardware configuration.
The quality of communication service between the receiving device and transmitting device may also vary depending upon the medium of transmission (e.g. radio waves, copper wire, etc.) and/or the priority given the transmission (e.g. different communications may be given different priorities thereby improving the quality of service provided to one at the expense of the other). Further, the way a particular medium is used by the communication mechanism and user may affect the quality of service (ie: having the recipient of each packet of transmitted information check for errors and return a positive or negative acknowledgement to the sender may increase reliability at a cost of increased latency). Also, routers and switches may be utilized to control the multifunctioning services of the communication mechanism to decrease latency without significant affects on reliability.
A selection of the communication mechanism at the time communication is to begin provides several benefits: the communicating systems get the qualities they require, the resources used for communication are more fully used, and new communication resources (hardware and software) can be installed/exploited without requiring changes to the system that will use those resources (ie: required changes to the application software).
In the past, quality of communication service has typically been defined by requiring one or more of the following: a specific medium, qualitative specifications and/or token-bucket specifications. A medium-specific specification is limited to one physical communication medium. For example, xe2x80x9cOC-3xe2x80x9d is a quality of service (in fact, a bandwidth, in bits per second) that makes sense for the SONET (Synchronous Optical Network) medium, but is meaningless in, for example, a BISDN (Broadband Integrated Services Digital Network). Thus there is a need for a device that is capable of defining quality of service independent of the medium being utilized.
Another medium-specific specification may require that the communication service be provided of the same quality that would be obtained if no other systems were using the medium. Such specifications suffer from the fact that they may become meaningless when the transmission medium is changed, and they are useless when several media are used to transmit a message.
Qualitative specifications are also limited in effectiveness. Qualitative specifications are expressed using a few terms such as xe2x80x9cbest effortxe2x80x9d and xe2x80x9curgentxe2x80x9d and may provide little assurance to the transmitting system that the subjective standard will be interpreted the same by the receiving system. Also, qualitative specifications have no verifiable semantics, and are therefore applicable only to problem domains where such vagueness and uncertainty is acceptable.
A token-bucket specification has precise semantics and is independent of any communication medium. However, token-bucket specifications are limited to a very narrow range of communication possibilities. A token-bucket is a particular form of communication traffic specification consisting of a xe2x80x9ctoken ratexe2x80x9d r and a xe2x80x9cbucket sizexe2x80x9d b. The token-bucket specification allows several systems to be connected and communicating with a single receiving system. The r parameter specifies the continually sustainable data rate of the receiving system, while the b parameter specifies the extent to which the data rate can exceed the sustainable level for short periods of time. The communication traffic must obey the rule that over all time periods, the amount of data sent cannot exceed rT+b, where T is the length of the time period. Evidently, token-bucket specifications cannot allow for common traffic patterns, such as strictly periodic events, or completely random (Poisson) events.
Other past devices have defined quality of communication service and load in terms of a specific quantity or number. For example, the values of latency, inter-service time, message size, and the like have been defined as constants. In some cases this is appropriate, as when messages of a known and constant size will be sent on a rigidly periodic schedule; however, a requirement to use a constant or single value to define the quality of service has required the application defining the quality of service to use worst-case values, resulting in poor resource utilization.
Also, past communication systems have not allowed the transmitting system to adequately define its requirements for quality of communication service prior to establishing a communication link with the receiving system. The present invention meets these and other needs that will become apparent from a review of the description of the present invention.
A system for determining whether an interface is capable of fulfilling a quality of service demand of an application is provided by the device and method of the present invention. The present invention includes an interface to an application, wherein the interface is capable of linking or xe2x80x9cnegotiatingxe2x80x9d with a plurality of applications and also performing services for the applications. The initial communications or requests sent from each application to the interface include a demand specifier that defines a required quality of service to be provided by the interface. A capability of the interface to provide the required quality of service is determined upon initiating a link or negotiation between the interface and the application. Without limitation, the device and method of the present invention may find application in networked computers, telecommunication links, aerospace and other applications that include linked devices wherein one device performs a service for the other. The device and method of the present invention may be utilized but is not limited to use in networks utilizing Asynchronous Transfer Mode (ATM).
The form of the demand specifier does not depend upon system requirements or medium linking the interface and application. The demand specifier includes a probability assertion, which may express or require a predefined maximum acceptable latency between requesting a service and performance of the service, a predefined minimum reliability of the link between the interface and the applications, and/or a predefined required security of the link. The probability assertion of the demand specifier is defined by a pair of density bounds, wherein the pair of density bounds may express a predefined maximum acceptable latency between requesting a service and performance of the service, a predefined minimum reliability of the link between the interface and the applications and/or a predefined required security of the link.
In use, a demand specifier is incorporated within the application, wherein the demand specifier defines a required quality of service to be performed by an interface. An initial link or negotiation between an application and interface is undertaken. Upon initializing the negotiation or link between the application and interface, the interface determines whether it is capable of performing the required quality of service of the application as defined by the demand specifier. Significant is the fact that the demand specifier does not depend upon system requirements of the interface. The negotiation or initial link is terminated between the interface and application if the interface is not capable of performing the quality of service required by the application. If the interface is capable of meeting the demand specifier of the application, then the communication link or xe2x80x9ccontractxe2x80x9d between the application and interface is established.
The advantages of the present invention should become readily apparent to those skilled in the art from a review of the following detailed description of the preferred embodiment especially when considered in conjunction with the claims and accompanying drawings in which like numerals in the several views refer to corresponding parts.